Answer:
The efficient level of security is 4 hours of security.
The equilibrium may not be sustainable.
Explanation:
In order to calculate the efficient level of security we would Set MB=MC i.e. guard's wage for net benefit maximization.
Hence, 100/(1+S)=20
20*(1+S)=10
1+S=5
S=4
Therefore, 4 hours of security is needed . The efficient level of security is 4 hours of security.
In the followig case Security guards is public good in this case, Public good is non-excludable and non-rivalrous. People cannot be stopped from using it without paying for it. Payment for security guard is voluntary. So, equilibrium may not be sustainable.